Dragons are dual creatures that symbolize the unconscious. In dreams they sometimes represent the fear of death. In most magic ritual dragons are used as symbolic doors to other dimensions. 

A popular figure, the dragon in the center of the labyrinth symbolizes the evil part of the unconscious (shadow). 

The dragon in the tower

The myth of the hero that delivers the princess from a tower guarded by dragon symbolizes the freedom of the young male who masters his anima (the princess) and the regressive forces of the mother to access plain relations with women. The tower is the symbol of the phallus . 

St Antony from Egypt (251-356 AC) had terrible visions of dragons and other monsters sent by the Devil.  In the case of temptations, the dragon often represents the woman and the prostitute, forbidden to the saint/monk. 

The amphisbaena is a two-headed dragon which heads are always in conflict. It represents the inner struggle between the conscious mind and the destructive forces of the unconscious (shadow). 

Mircea Eliade interprets the act of eating as a regressus in uterum which precedes a second birth . It is linked with knowledge and wisdom which are virtues of the original and ancient Dragon. When  the hero is swallowed by the monster (giant, dragon, …) he gains wisdom and knowledge of the secrets of nature.